Blog feed tag same as content, not the description

My blog feed is putting the first sentences of the blog in the tag. So when I use the merge tag in Mailchimp, I get the first sentences of the blog.

This is the same thing that is showing in the tag as well. I want what I put in the post description box to be what shows in the tag.

I write a summary of my blog and I put it in both the post description box and the meta description box. That’s what should go in the tag of feed.

For example, here is what is in the post description box for my most recent blog: Too many boring nonfiction books exist. Don’t add to the pile. Instead, write a good nonfiction by making your book more reader friendly, using these tips.

But you can see in the feed, it shows the first few sentences: “Confession: I rarely read ….”

The page I need help with: [log in to see the link]